I have an Arduino UNO setup with a SIM900 Shield. I want to make http/s requests using AT commands. I can already perform GET requests via http. But i can’t get them to work with https. Please help me find the issue.

I am trying to perform a GET request to the following URL: https://worldtimeapi.org/api/timezone/America/Vancouver/

By executing the following AT-Commands

// first i reset the services and connection
AT+HTTPTERM  -> OK
AT+CIPSHUT   -> OK
AT+SAPBR=0,1 -> OK

// then i reopen the connection and initialize the http service
AT+SAPBR=3,1,"Contype","GPRS"         -> OK
AT+SAPBR=3,1,"APN","internet.blau.de" -> OK
AT+SAPBR=1,1                          -> OK
AT+HTTPINIT                           -> OK
AT+HTTPPARA="CID",1                   -> OK

// then i initialize the https request
AT+HTTPPARA="URL","https://worldtimeapi.org/api/timezone/America/Vancouver/" -> OK
AT+HTTPSSL=1                                                                 -> OK

// but when performing the request, i receive an error response with code 601
AT+HTTPACTION=0 -> OK +HTTPACTION:0,601,0

When performing the request like this but with http (using http protocol in url and skipping the HTTPSSL=1 command) i receive a 200 response with the expected body.

According to some other posts and sources i found while investigating, 601 means connection issues. But i can establish the connection using my browser or Postman. And when looking up the connection status of my SIM900 everything seems fine as well.

AT+SAPBR=2,1 -> +SAPBR: 1,1,"10.217.95.14"
AT+SAPBR=4,1 -> +SAPBR: 
  CONTYPE: GPRS
  APN: internet.blau.de
  PHONENUM:    
  USER:       
  PWD:        
  RATE: 2     
AT+CGATT?    -> +CGATT: 1
AT+HTTPSSL=? -> +HTTPSSL: (0-1)